The enzymes of the galactose operon of E. coli are needed for utilization of galactose and normal cell morphology. The control of expression of the operon is complex. It is normally subjected to a negative control by gal repressor and a positive control by cyclic AMP. We have also shown that the galactose operon is and can be also subject to other control systems, including control of neighboring prophage genes. Our object is to determine the complete structure and to identify all the regulatory elements of the galactose operon of E. coli. These include the signals of initiation and termination of gene expression. We are also studying the expression of genes in bacteriophage lambda and P22 growth.